1. Field of the Invention
The present invention relates to an optical glass which contains a high proportion of rare earth ions and an optical element such as a lens obtained by forming the optical glass.
2. Description of the Related Art
As a high refractive index, low dispersion glass, a rare earth borate glass is known. In general, a high refractive index glass has high dispersion, while a low refractive index glass has low dispersion. An increased content of rare earths, however, allows a glass to have an increased refractive index while maintaining low dispersion. Examples of the glass with a high content of rare earths include glass disclosed in WO2010/053214, having a total content of La3+, Gd3+, Y3+, Sc3+ and Lu3+ of 15 to 50%.
The glass composition specifically disclosed in WO2010/053214, however, has a maximum content of rare earths of 38.8 cat. %, merely achieving a refractive index nd of 1.88 and an Abbe number of νd of 41.2. Accordingly, there still exists a problem of difficulty in producing a high refractive index, low dispersion glass.